Milling head for a ball track milling cutter, ball track milling cutter having a milling head of this type, method for producing a cutting edge for a ball track milling cutter, computer program product for carrying out a method of this type, data carrier having a computer program product of this type, and grinding machine for carrying out the method

ABSTRACT

A milling head for a ball track milling cutter includes an imaginary center axis, a first, working-side end and a second, clamping-side end opposite the first end when viewed along the central axis, and comprising at least one geometrically defined cutting edge, extending along a cutting edge profile of the cutting edge from a first cutting edge end facing the first end of the milling head in the direction of the second end of the milling head up to a second cutting edge end facing the second end of the milling head, wherein at least one cutting edge is formed as an intersecting line between the rake face associated with at least one cutting edge and a first flank face associated with at least one cutting edge, wherein at least one cutting edge is assigned a negative rake angle, a first clearance angle and a wedge angle. It is provided that a value of the negative rake angle in the region of the first cutting edge end has a different value than in the region of the second cutting edge end, that the first clearance angle in the region of the first cutting edge end has a different value than in the region of the second cutting edge end, and that the wedge angle along the cutting edge profile is constant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Phase of InternationalApplication No. PCT/EP2018/056588, filed Mar. 15, 2018, which claims thebenefit of German Patent Application No. 10 2017 204 369.5, filed Mar.16, 2017, and German Patent Application No. 10 2017 206 144.8, filedApr. 10, 2017. The entire disclosures of the above applications areincorporated herein by reference.

The invention relates to a milling head for a ball track milling cutter,a ball track milling cutter with this type of milling head, a method forproducing a cutting edge for a ball track milling cutter, a computerprogram product for performing the method, a data carrier with thecomputer program product, and a grinding machine for carrying out themethod.

A ball track milling cutter of the type mentioned here is known, forexample, from the German published patent application DE 10 2014 208 125A1. A milling head for such a ball track milling cutter has an imaginarycenter axis and one working-side end and a second clamping-side endopposite the first end when viewed along the center axis. The millinghead also has at least one geometrically defined cutting edge which,starting from a first cutting edge end facing the first end of themilling head, extends in the direction of the second end of the millinghead up to a second cutting edge end facing the second end of themilling head along a cutting edge profile. At least one cutting edge isformed as an intersecting line between a rake face and a flank face,which are respectively associated with the cutting edge, and whichintersect along the cutting edge. At least one cutting edge is alsoassigned a negative rake angle, a first clearance angle and a wedgeangle.

Known milling heads have a limited service life, wherein in the regionof the at least one cutting edge sharp edges form, in particular withprolonged use, which in turn leads to chipping along the cutting edgeprofile. Wear is not uniformly distributed along the cutting edgeprofile, but instead has a pronounced wear profile. In the region of thesecond cutting edge end the at least one cutting edge wears much fasterand more than in the region of the first cutting edge end.

It is an object of the invention to provide, a milling head for a balltrack milling cutter, a ball track milling cutter with such a millinghead, a method for producing a cutting edge for a ball track millingcutter, a computer program product for performing such a method, a datacarrier with such a computer program product, and a grinding machine forimplementing the method, wherein the mentioned disadvantages do notoccur.

The object is achieved by providing the objects in the independentclaims. Advantageous embodiments are described in the dependent claims.

The object is achieved in particular by providing a milling head for aball track milling cutter of the type described above, which ischaracterized in that the negative rake angle in the region of the firstcutting edge end, in particular at the first cutting edge end, has adifferent value than in the region of the second cutting edge end, inparticular at the second cutting edge end. The first clearance anglealso has a different value in the region of the first cutting edge end,in particular on the first cutting edge end, than in the region of thesecond cutting edge end, in particular on the second cutting edge end.The wedge angle is constant along the cutting edge profile. Thus, whilethe wedge angle along the cutting edge profile does not change from thefirst cutting edge end to the second cutting edge end, the negative rakeangle on the one hand and the clearance angle on the other hand have avalue in the region of the first cutting edge end which is differentfrom a value that is given in the region of the second cutting edge end.In this way, the geometric configuration of at least one cutting edge isin different regions along its cutting edge profile adapted to arespective current engagement situation during the machining of aworkpiece, whereby the wear of the cutting edge is reduced andvibrations during machining of the workpiece are advantageously reduced.This also contributes to a longer service life of the milling head.

Milling heads and ball track milling cutters of the type mentioned hereare used in particular for the production of joints of universal shafts,in particular for the production of ball running surfaces of homokineticjoints. They serve in particular to produce ball treads, also referredto as ball tracks, both in the outer part of such a joint and in itsinner part. Such a milling head is used for machining a ball runningsurface at a certain lead angle relative to a workpiece to be machined.The lead angle is the angle which the imaginary center axis of themilling head assumes with respect to a tangent applied to a momentarypoint of contact of the cutting edge of the milling head with theworkpiece surface. At least one cutting edge touches the workpiece to bemachined punctiform or at least approximately punctiform in the regionof the point of contact, which is not constant during the machining ofthe workpiece on the cutting edge, but instead is displaced along thecutting edge profile. This results in particular from the final leadangle of the milling head on the one hand, and from the specificrelative movement between the milling head and the workpiece to bemachined, which is provided for generating a ball running surface in theworkpiece, on the other. As this occurs, a relative rotation takes placeabout the imaginary center axis for generating the ball running surfacealong an imaginary circumference on the one hand and on the other hand,a suitable relative displacement between the workpiece and the millinghead to produce the ball running surface along a length on thesame—perpendicular to the imaginary circumference occurs. It isparticularly preferable that the milling head is rotated about theimaginary center axis, while at the same time the workpiece—preferablyin an elliptical motion—is guided around the imaginary center axis ofthe milling head, such that the ball running surface is formed along itsentire length. While the ball running surface is being processed, atleast one cutting edge enters into the workpiece to be machined from thefirst cutting edge end, whereby the point of contact on the cutting edgeshifts from the first cutting edge end towards the second cutting edgeend as machining continues. In the place where the cutting edge entersinto the material of the in particular semi-circularly designed balltread, and where it emerges from this material again, skips in theapplied cutting force occur, which are also referred to as interruptionsin the cutting force, and contribute to unwanted vibrations in themilling head. This has a negative effect on both chip formation andservice life. The adapted geometry proposed here of at least one cuttingedge allows its adaption to the displacement of the point of contact inthe course of workpiece machining and at the same time a reduction inthe vibrations described above, so that overall the service life of themilling head is improved.

It is possible that the milling head has only one and exactly onegeometrically defined cutting edge. However, it is also possible inanother embodiment that the milling head has a multitude ofgeometrically defined cutting edges, in particular two geometricallydefined cutting edges, three geometrically defined cutting edges, fourgeometrically defined cutting edges, or five geometrically definedcutting edges. Of course, a larger number of geometrically definedcutting edges is also possible. Most preferably, however, the millinghead has four geometrically defined cutting edges. Preferably, allgeometrically defined cutting edges on the milling head are identicaland in particular formed as is explained here and below for at least onegeometrically defined cutting edge.

The milling head can be formed in one piece with other elements of aball track milling cutter, in particular with a ball track millingcutter main body, so that this is in particular a milling head for aball track milling cutter. However, it can also be formed in severalparts with the remaining parts of the ball track milling cutter, where,for example, it can be connected with the ball track milling cutter mainbody via an interface, such as by means of a thread having a subsequentcentering cone and a plane surface for positionally accurate fixation ofthe milling head on the ball track milling cutter main body surroundingthe centering cone in the circumferential direction. Such one-piece andmulti-piece designs, and corresponding interfaces in particular, areknown, so they will not be discussed in detail.

A working-side end of the milling head is understood in particular to bethe end—viewed along the imaginary center axis—that is intended to facethe workpiece during machining of a workpiece by the milling head. Aclamping-side end of the milling head, in contrast, is understood tomean—viewed along the central axis—an end facing away from the workpieceduring machining of a workpiece, this end being associated with aclamping section of the milling head or the ball track milling cutter.As explained above, the milling head is adapted to be connected to theclamping section with a ball track milling cutter main body. The balltrack milling cutter may in turn be adapted to be connected to asuitably designed clamping section with other tool elements, such asadapters, spacers, extensions, etc., or directly to a machine spindle.For this purpose, the ball track milling cutter may in particular have aclamping shaft that is suitable for being clamped into another tool partand/or a machine spindle. Such a clamping shaft may, for example, bedesigned cylindrical, conical, for example, as a Morse taper or a hollowshaft taper (HST).

The fact that the rake face is associated with at least one cutting edgemeans, in particular, that the rake face adjoins at least one cuttingedge directly. Accordingly, the first flank face connects directly tothe cutting edge. This results in particular from the fact that thecutting edge is formed as an intersecting line of the rake face with thefirst flank face.

The fact that at least one cutting edge is assigned a negative rakeangle means in particular that the rake face has a negative rake angle.Such a negative rake angle is particularly advantageous for machininghard materials that are machined with a cutting material with highhardness and temperature resistance. Typically, workpieces of the typediscussed here are machined in already hardened form with the millinghead. Higher cutting forces and shorter chips can be achieved with anegative rake angle. Suitable hard cutting materials, because of theirinternal crystalline structure, have the property of being resistant tocompressive stresses that occur at a negative rake angle. At the sametime, they also have a high hardness and temperature resistance. Incontrast, a positive rake angle would produce a tensile stress when chipbreakage occurs, which would cause a corresponding hard cutting materialto fail very quickly. Specifically, such hard cutting materials exhibitpoor behavior in response to tensile stresses, in particular a lowinternal resistance of the material to stress. Therefore, with positiverake angles, they tend to easily chip on the cutting edge.

Furthermore, it should be noted that the wedge angle for machining hard,brittle materials should be as great as possible in order to guaranteethe necessary robustness in the machining of materials with highstrength and hardness.

The rake angle is an angle that the rake face with an imaginary plane inwhich the cutting edge extends, and which is locally perpendicular to aworkpiece surface machined by the cutting edge. The rake angle has apositive value when the rake face is reset relative to the imaginaryplane, i.e. when viewed against the machining direction—while the rakeangle is associated with a negative sign when the rake face—when viewedin the machining direction—precedes the cutting edge, i.e. is positionedin the machining direction in front of the imaginary plane.

The clearance angle is an angle that the flank face forms with amachined workpiece plane or a tangent plane applied to the machinedworkpiece in the region of the cutting edge, the cutting edge also lyingin this workpiece plane or tangential plane. The workpiece plane ortangential plane used for determining the clearance angle on the onehand and the imaginary plane used to determine the rake angle areperpendicular to one another and intersect in the cutting edge. Inparticular, the clearance angle ensures that the milling head isreleased from the machined workpiece surface, minimizing friction andheating between the cutting edge and the machined material.

The wedge angle is the angle that both the rake face and the first flankface form together.

It is the general rule that the rake angle—taking into account the signassigned to it—the first clearance angle and the wedge angle always addup to 90°—based on a full circle of 360°.

The wedge angle can therefore be calculated from the rake angle—takinginto account its sign—and the first clearance angle. Conversely, thefirst clearance angle results from the wedge angle and the rake angle.

According to a further embodiment of the invention, it is provided thatno two different points along the cutting edge exist on at least onecutting edge, where at least one cutting edge has identical values forthe rake angle and/or identical first clearance angles. This means, inparticular, that the value of the negative rake angle and/or the firstclearance angle is/are not the same at any two different points alongthe cutting edge profile on the cutting edge. The value of the negativerake angle is therefore different at each point along the cutting edgeprofile. Alternatively or additionally, the clearance angle is differentat each point along the cutting edge profile. This leads to aparticularly favorable geometric cutting geometry for reducingvibrations occurring during the machining of a workpiece and forincreasing the service life of the milling head.

According to a further embodiment of the invention, it is provided thatthe value of the negative rake angle and/or the first clearance anglevary/varies continuously along the cutting edge profile. In thiscontext, a continuous variation is understood as meaning, in particular,a continuous change, in particular a continuous and differentiablechange, of the values for the value of the rake angle and/or the firstclearance angle, wherein, in particular, no jumps occur in thecorresponding values. Particularly preferably, the value of the negativerake angle and/or the first clearance angle along the cutting edgeprofile of at least one cutting edge change/changes linearly. Thus,abrupt changes in the cutting geometry are avoided, which has afavorable effect on the prevention of vibrations and an increasedservice life of the milling head.

According to a further embodiment of the invention, it is provided thatthe value of the negative rake angle in the region of the first cuttingedge end, in particular at the first cutting edge end, is lower than inthe region of the second cutting edge end, in particular at the secondcutting edge end. Alternatively or additionally, it is preferablyprovided that the first clearance angle in the region of the firstcutting edge end, in particular at the first cutting edge end, is lowerthan in the region of the second cutting edge end, in particular at thesecond cutting edge end. In this way, the durability and robustness ofthe cutting geometry is adjusted so that at least one cutting edge hashigher robustness along its cutting edge profile in the place where itwould otherwise be subject to increased wear, and is also designed foreasier cutting where it typically has less wear. Thus, the wear over theprofile of the cutting edge in particular can be made uniform, by whichmeans the overall service life of the free head is increased. Theconstant wedge angle along the profile of the cutting edge ensures thatthe robustness and stability of the cutting geometry are not decreasedanywhere in the cutting edge profile by a reduced wedge angle.

By changing the negative rake angle and the clearance angle along thecutting edge profile on the one hand and the constant wedge angle on theother hand, the cutting geometry is rotated, so to speak, in the profileof the cutting edge from the first cutting edge end to the secondcutting edge end—when viewed in the cross section. The rake face inparticular has a twisted profile along the cutting edge due to theprogressions of the rake angle and the clearance angle, a normal vectorof the rake face being twisted, so to speak, in the profile of thecutting edge from the first cutting edge end to the second cutting edgeend toward an outer circumference of the milling head. This produceshigher robustness in the cutting geometry, in particular in the regionof the second cutting edge end, that is to say where increased wearoccurs in conventional milling heads.

According to a further embodiment of the invention, it is provided thatthe value of the negative rake angle along the cutting edge profile—inparticular from the first cutting edge end to the second cutting edgeend—increases to the same extent to which the first clearance angle alsoincreases. The value of the rake angle thus increases in particular inthe same ratio as the value of the first clearance angle.

For the sake of clarification, it should be added that the negative rakeangle—everywhere in the cutting edge profile—becomes smaller andsmaller, i.e. it changes to more negative values as its value increasesfrom the first cutting edge end towards the second cutting edge end.

According to a further embodiment of the invention, it is provided thata width of the rake face in the region of the first cutting edge end, inparticular at the first cutting edge end, is greater than in the regionof the second cutting edge end, in particular at the second cutting edgeend. In this case, the width of the rake face preferably changescontinuously along the cutting edge profile from the first cutting edgeend to the second cutting edge end, preferably linearly with the cuttingedge profile in particular. In particular, the width of the rake facepreferably decreases continuously, in particular linearly, from thefirst cutting edge end to the second cutting edge end. This is theresult with a given contour of the cutting edge, that is to say with apredetermined cutting edge profile from the development of the rakeangle on the one hand and the first clearance angle on the other handalong the cutting edge profile.

The rake face proposed here, variable with respect to its width andtwisted along its profile, is also referred to as a tracking negativechamfer. It enables, in the region of the second cutting edge end inparticular, increased robustness of the cutting geometry and thus animproved service life of the milling head with simultaneously reducedvibrations.

According to a further embodiment of the invention, it is provided thatthe width of the rake face in the region of the first cutting edge endis at most 0.4 mm, preferably at most 0.3 mm, wherein the width of therake face in the region of the second cutting edge end is at least 0.1mm, preferably at least 0.15 mm. With these values, the advantagesalready described are realized in a particular way.

According to a further embodiment of the invention, it is provided thatthe cutting edge profile is straight, curved and/or spirally formed. Thecutting edge profile may in particular be aligned parallel to theimaginary center axis, or form a finite angle with the imaginary centeraxis. It is possible that this angle is varied or constant along thecutting edge profile. The embodiment of the cutting edge profiledescribed here relates in particular to an imaginary projection of theactual cutting edge profile in space onto an imaginary cylindricalperipheral surface which extends concentrically around the center axis.In fact, the cutting edge profile is always curved because the millinghead is at least formed hemispherically or approximately hemisphericallyin the region of at least one cutting edge. However, this curvaturedisappears when projected onto an imaginary, cylindrical circumferentialsurface about the center axis, so that it is particularly easy to judgein this projection whether the cutting edge is aligned parallel to thecentral axis, at an angle to the central axis, or spirally formed aroundthe central axis.

Overall, the milling head thus has, at least in the region of itsworking-side end, ahemispherical or at least approximately hemisphericalgeometry, the curvature of which at least one cutting edge follows,wherein in particular in this way a ball track can be produced, inparticular with a diameter corresponding to the diameter of theimaginary hemisphere.

According to a further embodiment of the invention, it is provided thatthe amount of the negative rake angle in the region of the first cuttingedge end, in particular at the first cutting edge end, is from at least10° to at most 19°, preferably from at least 12° to at most 17°,preferably from at least 14° to at most 16°, preferably 15°.Alternatively or additionally, the value of the negative rake angle inthe region of the second cutting edge end, in particular at the secondcutting edge end, is preferably from at least 20° to at most 30°,preferably from at least 22° to at most 28°, preferably from at least24° to at most 26°, preferably 25°.

Alternatively or additionally, the first clearance angle in the regionof the first cutting edge end, in particular at the first cutting edgeend, is from at least 5° to at most 10°, preferably from at least 6° toat most 8°, preferably 7°. Alternatively or additionally, the firstclearance angle, preferably in the region of the second cutting edgeend, preferably at the second cutting edge end, from at least 15° to atmost 20°, preferably from at least 16° to at most 18°, preferably 17°.

At the values specified here for the value of the negative rake angleand/or the first clearance angle, the advantages of the milling headalready described above are realized in a particular way.

According to a further embodiment of the invention, it is provided thatthe first flank face circumferentially adjoins a second flank face,which is associated with a second clearance angle. In this case, theterm “peripherally” refers in particular to a circumferential line whichconcentrically surrounds the imaginary center axis. The second flankface is in particular immediately adjacent to the first flank face,wherein the first flank face is positioned between the cutting edge andthe second flank face.

Preferably, the second clearance angle is greater everywhere along thecutting edge profile than the first clearance angle.

According to a further embodiment of the invention, it is provided thatthe second clearance angle is constant along the cutting edge profile.In particular, it is preferably from at least 16° to at most 21°,preferably from at least 17° to at most 19°, preferably 18°.

The second flank face, which in comparison to the first flank facedecreases more sharply—when viewed in the machining direction—enablesimproved clearance and reduced friction as well as heat between thecutting edge and the machined material while maintaining a robustcutting geometry.

According to a further embodiment of the invention it is provided thatthe milling head has a main body. It is possible that at least onecutting edge is formed directly on the main body, in particular machinedfrom the main body. Alternatively, it is possible that at least onecutting edge is formed on a cutting insert connected to the main body.

The main body preferably has a solid carbide or consists of a solidcarbide. In the case in which the cutting edge is formed directly on themain body, the main body preferably has a hard material layer at leastpartially applied, in particular pressed onto the solid carbide,preferably made from cubic boron nitride (CBN), polycrystalline cubicboron nitride (PCBN), or polycrystalline diamond (BKD), wherein at leastone cutting edge formed on the hard material layer is in particularmachined out of the hard material layer. If, in contrast, at least onecutting edge is formed on a cutting insert connected to the main body,the main body may consist in particular of solid carbide, wherein thecutting insert preferably comprises a hard material or is formed from ahard material, wherein the cutting insert in particular comprises amaterial or consists of a material selected from a group consisting ofcubic boron nitride (CBN), polycrystalline cubic boron nitride (PCBN),and polycrystalline diamond (PCD).

The cutting insert is preferably connected to the main body inparticular by soldering, preferably by brazing. In particular, it ispossible that the cutting insert is soldered into the main body.

It is also possible in principle that the cutting insert is attached tothe main body in a different manner, for example by screw clamping,whereby it can be exchanged for a new cutting insert especially easilyafter reaching the end of a service life. In this case, however, due tothe less stable arrangement of the cutting insert compared to solderingand the resulting inaccuracies when exchanged, shorter service liferesults. In addition, exchangeable cutting inserts may lead to increasedinaccuracies in the machining and ultimately increased tolerancedeviations in the machined workpiece. By comparison, firmly solderedcutting inserts lead to a significant increase in service life and avoidinaccuracies when exchanged, so that the machining accuracy increasesand the achievable tolerances on the machined workpiece can be improved.

The object is also achieved by providing a ball track milling cutterthat has a milling head according to one of the embodiments describedabove. In particular, the advantages that have already been explained inconnection with the milling head are realized in connection with theball track milling cutter. As also already explained, the milling headmay be formed in one piece with remaining parts of the ball trackmilling cutter, in particular with a ball track milling cutter mainbody. But it is also possible that the milling head is formed in severalpieces with the ball track milling cutter base body and can be attachedto it by means of a suitable interface. This embodiment has theadvantage that the milling head can be replaced at the end of itsservice life in a simple manner, without the ball track milling cuttermain body needing to be disposed of and replaced at the same time.

The object is also achieved by providing a method for producing acutting edge for a ball track milling cutter, in which the cutting edgeis produced by grinding directly on a main body of a milling head or ona cutting insert for a milling head, wherein the cutting edge isproduced as an intersecting line between a rake face and a flank face,wherein the cutting edge is formed with a negative rake angle whosevalue is different in the region of a first cutting edge end facing anintended working-side end of the milling head than in the region of asecond cutting edge end facing an intended clamping-side end of themilling head, wherein the cutting edge is formed with a clearance anglethat has a different value in the region of the first cutting edge endthan in the region of the second cutting edge end, and wherein thecutting edge is formed with a wedge angle, which is constant along acutting edge profile of the cutting edge between the first cutting edgeend and the second cutting edge end. In connection with the method, theadvantages already explained in connection with the milling head on theone hand and the ball track milling cutter on the other hand are inparticular realized.

In particular, the main body or the cutting insert is ground, whereinthe cutting edge is produced by grinding the main body or the cuttinginsert as an intersecting line between the rake face and the flank face.

In particular, the cutting edge is made by grinding at least one surfaceselected from the rake face and the flank face, preferably by grindingthe rake face and the flank face, as an intersecting line between theflank face and the rake face.

If the cutting edge is produced on a cutting insert for a milling head,this is preferably done according to a first embodiment of the methodafter fastening the cutting insert to a milling head, in particularafter soldering the cutting insert onto the milling head or soldering itinto the milling head. The cutting insert(s) is/are preferably brazed tothe milling head. Alternatively, according to another embodiment of themethod, it is possible for the cutting insert to be ground prior toattachment to the milling head, thereby producing the cutting edge.However, it is possible that in this case, the cutting edge issubsequently processed after attaching the cutting insert to the millinghead, in particular to ensure the dimensional accuracy of the cuttingedge.

By using the method, in particular by producing the cutting edgedirectly on the main body of the milling head or on the cutting insert,a milling head according to the invention or a milling head according toone of the embodiments described above is preferably obtained. Thecutting insert can be attached to the milling head after grinding ifnecessary, in particular by soldering, preferably by brazing.

The object is also achieved by providing a computer program product withmachine-readable instructions for carrying out a method according tothis invention or method according to one of the previously describedembodiments when the computer program product is running on a computingdevice set up for controlling a grinding machine and preferablyoperatively connected with the grinding machine for controlling thesame. Due to the machine-readable instructions, the computing devicethen controls in particular the grinding machine such that the cuttingedge is produced. In connection with the computer program product, inparticular, the advantages that have already been explained inconnection with the milling head and/or the ball track milling cutterresult.

The computer program product comprises in particular machine-readableinstructions on the basis of which a main body of a milling head or acutting insert for such a milling head arranged on or in the grindingmachine is ground, wherein the cutting edge is produced by grinding anintersecting line between a rake face and a flank face, in particular bygrinding at least one face, selected from the flank face and the rakeface with the grinding machine. Preferably, the flank face and the rakeface are ground by the grinding machine.

The object is also achieved by providing a data carrier on which acomputer program product according to the invention or a computerprogram product according to one of the embodiments described above isstored. The data carrier is preferably designed as a volatile ornon-volatile data carrier. The data carrier may in particular be a mainmemory of a computing device, a read-only memory, in particular a harddisk or hard disk device of the computing device, or a mobile datacarrier, for example tape storage, a floppy disk, a CD-ROM, a DVD, a USBstick, a memory card, or similar. The data carrier may also be designedas a data cloud, i.e. in particular as a network memory of a multitudeof computing devices, in particular as a Cloud.

In particular in connection with the data carrier, the advantagesalready explained in connection with the milling head or the ball trackmilling cutter are realized.

Finally, the object is also achieved by providing a grinding machine setup for carrying out a method according to this invention or a methodaccording to one of the previously described embodiments. In particularin connection with the grinding machine, the advantages that havealready been explained in connection with the milling head or the balltrack milling cutter are realized.

The grinding machine preferably has a computing device that runs acomputer program product according to the invention or a computerprogram product according to one of the embodiments described above.Alternatively or additionally, the grinding machine preferably has adata carrier according to the invention or a data carrier according toone of the previously described embodiments.

The method is in particular designed to produce a milling head accordingto the invention or a milling head according to one of the embodimentsdescribed above. In this respect, the method preferably has at least onemethod step, which is based on at least one feature or a combination offeatures of the milling head according to this invention or a millinghead according to one of the described embodiments. In particular,method steps that have been explained explicitly or implicitly inconnection with the milling head, preferably individually or incombination with each other, comprise steps for a preferred embodimentof the method.

The invention will be explained in more detail below with reference tothe drawing. In the figures:

FIG. 1 shows a detailed depiction of an embodiment of a milling head fora ball track milling cutter;

FIG. 2 shows a first detailed cross-sectional view along a first sectionline A-A shown in FIG. 1, and

FIG. 3 shows a second detailed cross-sectional view along a secondsection line B-B shown in FIG. 1.

FIG. 1 shows a detailed depiction of a first embodiment of a millinghead 1 for a—not shown beyond milling head 1—ball track milling cutter3. The milling head 1 has an imaginary center axis M, which correspondsto a rotational axis of the milling head 1 and also of the ball trackmilling cutter 3 during the intended machining of a workpiece, notshown. The milling head 1 and in particular also the ball track millingcutter 3 is/are therefore preferably rotated about the center axis Mduring the machining of a workpiece.

The milling head 1 has a first, working-side end 5 and a second,clamping-side end 7 opposite the first end 5 along the center axis M,which clamping-side end 7 is no longer shown here on the detailedillustration of FIG. 1, wherein the first end 5 faces the workpieceduring the machining of a workpiece as intended, wherein the second end7 faces a clamping portion of the ball track milling cutter 3 or has aclamping portion of the milling head 1.

The milling head 1 also has at least one geometrically defined cuttingedge, here a total of four geometrically defined cutting edges, only oneof which is designated by the reference numeral 9 for better clarity.

Everything that is explained below for the geometrically defined cuttingedge 9, which is explicitly designated here, applies in just the sameway to the other three geometrically defined cutting edges of themilling head 1, which are not specifically designated for the sake ofbetter clarity. The four geometrically defined cutting edges 9 aretherefore all identically designed. Therefore for the sake ofsimplicity, only one geometrically defined cutting edge 9 will bedescribed in detail below.

The geometrically defined cutting edge 9 extends, starting from a firstcutting edge end 11 facing the first end 5, in the direction of thesecond end 7 to a second cutting edge end 13 along a cutting edgeprofile, wherein the term “cutting edge profile” describes the profileof the geometrically defined cutting edge 9 starting from the firstcutting edge end 11 to the second cutting edge end 13.

The cutting edge 9 is formed as an intersecting line between a rake face15 and a first flank face 17, which are respectively associated with thecutting edge 9. The rake face 15 has a negative rake angle. In additionto the negative rake angle, the cutting edge 9 is assigned a firstclearance angle and a wedge angle, which are explained in more detail inconnection with FIGS. 2 and 3.

In the milling head 1, it is in particular provided that a value of thenegative rake angle in the region of the first cutting edge end 11 willhave a different value than in the region of the second cutting edge end13, wherein the first clearance angle in the region of the first cuttingedge end 11 has a different value than in the region of the secondcutting edge end 13. The wedge angle is constant along the cutting edgeprofile from the first cutting edge end 11 to the second cutting edgeend 13.

In particular, the cutting edge 9 along the cutting edge profile doesnot have two mutually different points at which the values for thenegative rake angle and/or the first clearance angle would be equal.Particularly preferably, the value of the rake angle and/or the firstclearance angle vary continuously, in particular linearly along thecutting edge profile of the cutting edge 9.

The value of the negative rake angle is preferably smaller in the regionof the first cutting edge end 11, in particular at the first cuttingedge end 11, than in the region of the second cutting edge end 13, inparticular at the first cutting edge end 13. Alternatively oradditionally, the first clearance angle in the region of the firstcutting edge end 11, in particular at the first cutting edge end 11, ispreferably smaller than in the region of the second cutting edge end 13,in particular at the second cutting edge end 13.

The value of the negative rake angle increases along the cutting edgeprofile from the first cutting edge end 11 toward the second cuttingedge end 13, in particular to the extent that the first clearance anglealso increases. The value of the negative rake angle and the firstclearance angle thus increase in particular in the same ratio.

It is also already clear from FIG. 1 that the width of the rake face 15in the region of the first cutting edge end 11, in particular at thefirst cutting edge end 11, is greater than in the region of the secondcutting edge end 13, in particular at the second cutting edge end 13.The width of the rake face 15 also varies continuously along the cuttingedge profile, in particular it decreases linearly from the first cuttingedge end 11 to the second cutting edge end 13. The rake face 15 can alsobe referred to as a tracking negative chamfer.

Preferably, the width of the rake face 15 in the region of the secondcutting edge end 13 is at least 0.1 mm, preferably at least 0.15 mm,wherein the width of the rake face 15 in the region of the first cuttingedge end 11 is at most 0.4 mm, preferably at most 0.3 mm.

It is also clear from FIG. 1 that the rake face 15, starting from thefirst cutting edge end 11 up to the second cutting edge end 13,effectively assumes a twisted profile, an imaginary normal vector of therake face 15 extending from the first cutting edge end 11 to the secondcutting edge end 13 is rotated outwards in the direction of the outervicinity of the milling head 1.

It is possible that the cutting edge 9 has a straight, curved, and/orspiral course, in particular in a projection onto a cylindricalperipheral surface encompassing the center axis M. In particular, it maybe aligned parallel to the imaginary center axis or may comprise afinite angle with the same.

In the embodiment shown here, the milling head 1 has a main body 19,which preferably comprises solid carbide or consists of solid carbide.The cutting edge 9 here is formed on a soldered on cutting insert 21connected to the main body 19, in particular on main body 19—preferablyby brazing. In particular, a separate cutting insert 21 is provided foreach of the four cutting edges 9. This is preferably true regardless ofhow many cutting edges 9 the milling head 1 actually has. Therefore eachcutting edge 9 is always associated with its own cutting insert 21.

The cutting insert 21 preferably comprises or is made from a materialselected from a group consisting of cubic boron nitride (CBN),polycrystalline cubic boron nitride (PCBN), and polycrystalline diamond(PCD).

Alternatively, it is also possible that the cutting edge 9 is formeddirectly on the main body 19, in particular machined from it. In thiscase, the main body 19 preferably has a solid carbide body and a hardmaterial layer pressed onto the solid carbide body from which thecutting edge 9 has been machined. This hard material layer preferablycomprises a material or consists of a material selected from a groupconsisting of cubic boron nitride (CBN), polycrystalline cubic boronnitride (PCBN), and polycrystalline diamond (PCD).

FIG. 2 shows a detailed cross-sectional view according to a firstsection line A-A shown in FIG. 1. The first cross-sectional planeillustrated in FIG. 2 is positioned closer to the first cutting edge end11 than a second cross-sectional plane illustrated in FIG. 3, which isindicated in FIG. 1 by a second section line B-B, wherein the detailedcross-sectional view of FIG. 3 is positioned closer to the secondcutting edge end 13.

Identical and functionally identical elements are provided with the samereference signs so reference is made to the previous description in thisregard.

In FIG. 2, an imaginary workpiece plane 23 in particular, which can alsobe designed as a tangential plane to the machined workpiece, and animaginary plane 25 are shown, the imaginary plane 25 being perpendicularto the imaginary workpiece plane 23, and the imaginary workpiece plane23 and the imaginary plane 25 intersecting in the cutting edge 9. Duringthe machining of a workpiece, the cutting edge 9 touches the workpiece,in particular at a point of contact that lies both in the imaginaryworkpiece plane 23 and in the imaginary plane 25, wherein the imaginaryworkpiece plane 23 is designed in particular as a tangential plane tothe workpiece in the point of contact.

The rake angle 15 results as an angle that the rake face 15 forms withthe imaginary plane 25, depicted here numerically with the rake angleidentical angle α for the sake of simplicity, wherein the identitybetween the illustrated angle α and the rake angle results from simplegeometric considerations. Therefore in the following, for the sake ofsimplicity, the rake angle is also referred to as rake angle α.

An arrow P1 indicates a machining direction of the milling head 1 here,along which the cutting edge 9 is displaced relative to a workpiece. Itis clear that the rake face 15 of the imaginary plane 25 and the cuttingedge 9 lead in the machining direction. Therefore, the rake angle α isassigned a negative sign.

The first clearance angle β is the angle that the flank face 17 formswith the imaginary workpiece plane 23.

Finally, the wedge angle γ is the angle that the rake face 15 forms withthe flank face 17.

Here, the equation applies that the rake angle α—taking into account itssign—the wedge angle γ and the first clearance angle β add up to 90°,wherein the degree refers to a full circle of 360°.

For example, here the sum of the wedge angle γ and the first clearanceangle β is greater than 90° by the exact value of the negative rakeangle α, so that exactly 90° results when the value of the rakeangle—due to the negative sign, which is associated with the rakeangle—is subtracted from the sum of the wedge angle γ and the firstclearance angle β.

In FIG. 2, a width b of the rake face 15 is plotted.

As already mentioned, FIG. 3 shows a second detailed cross-sectionalview along the second section line B-B shown in FIG. 1.

A comparison of FIGS. 2 and 3 shows that both the value of the negativerake angle α and the value of the first clearance angle β are smaller inthe region of the first cutting edge end 11 than in the region of thesecond cutting edge end 13. In particular, they have the first valuesα1, β1 in the sectional plane according to FIG. 2, which are smallerthan the second values α2, β2 according to the sectional plane in FIG.3. However, the change of the rake angle α on the one hand and of theclearance angle β on the other hand is such that the wedge angle γ isconstant.

Overall, a comparison of FIGS. 2 and 3 also shows that the cuttinggeometry is twisted, so to speak, from the first cutting edge end 11 tothe second cutting edge end 13, here, in the clockwise direction.

At the same time, given a predetermined cutting edge profile of thecutting edge 9, the width b of the rake face 15 decreases from the firstcutting edge end 11 to the second cutting edge end 13. In that regard,the rake face 15 in FIG. 2 has a first, greater width b1 and in FIG. 3,a second, smaller width b2.

The value of the negative rake angle α described here in the region ofthe first cutting edge end 11, in particular at the first cutting edgeend 11, is preferably at least 10° to at most 19°, preferably at least12° to at most 17°, preferably at least 14° to at most 16°, preferably15°. In the region of the second cutting edge end 13, in particular atthe second cutting edge end 13, it is preferably from at least 20° to atmost 30°, preferably from at least 22° to at most 28°, preferably fromat least 24° to at most 26°, preferably 25°.

In the region of the first cutting edge 11, in particular at the firstcutting edge end 11, the first clearance angle β is preferably from atleast 5° to at most 10°, preferably from at least 6° to at most 8°,preferably 7°. In the region of the second cutting edge end 13, inparticular on the second cutting edge end 13, it is preferably from atleast 15° to at most 20°, preferably from at least 16° to at most 18°,preferably 17°.

In a manner not shown, a second flank face adjoins the first flank face17 on the circumference, to which a second clearance angle is assigned.This second clearance angle is preferably greater than the firstclearance angle β along the cutting edge profile of the cutting edge 9,and particularly preferably is constant along the cutting edge profile.It preferably has a value from at least 16° to at most 21°, preferablyof at least 17° to at most 19°, preferably of 18°.

The cutting geometry of the milling head 1 shown here proves to beparticularly robust, whereby, in particular, unified wear is createdover the profile of the cutting edge 9, so that the service life of themilling head 1 is increased. In addition, vibrations in the machining ofa workpiece are reduced, which also has an advantageous effect on theservice life of the milling head 1.

The cutting edge 9 is preferably produced by directly grinding the mainbody 19 or the cutting insert 21, in particular by grinding at least onesurface selected from the rake face 15 and the first flank face 17.Preferably, both the rake face 15 and the first flank face 17 are groundto produce the cutting edge 9 as a intersecting line between the rakeface 15 and the first flank face 17.

If the cutting insert 21 is ground, this preferably takes place when thecutting insert 21 is already fastened to the main body 19.Alternatively, the cutting insert can also be ground prior to attachmentto the main body 19.

The milling head 1 is preferably obtained by manufacturing the cuttingedge 9. If needed, it additionally only requires a fastening, inparticular a soldering, of the cutting insert 21 to the main body 19 ifthe cutting insert 21 is ground prior to attachment to the main body 19.

The grinding is preferably carried out with an automated, in particularprogrammable, grinding machine. In particular, a computer programproduct is provided for controlling the grinding machine, which hasmachine-readable instructions on the basis of which a previouslydescribed method for producing the cutting edge 9 on the grindingmachine is carried out when the computer program product runs on acomputer set up to drive the grinding machine.

In that regard, the invention also includes a data carrier with such acomputer program product, as well as a grinding machine, which is set upfor carrying out the method.

The invention claimed is:
 1. A milling head for a ball track millingcutter, the milling head comprising: an imaginary center axis; a firstend being a working-side end and a second end being a clamping-side endopposite the first end relative to the imaginary center axis; and atleast one geometrically defined cutting edge extending from a firstcutting edge end facing the first end of the milling head in a directionof the second end of the milling head to a second cutting edge endfacing the second end of the milling head extending along a cutting edgeprofile of the at least one cutting edge, wherein the at least onecutting edge is an intersecting line between a rake face associated withthe at least one cutting edge and a first flank face associated with theat least one cutting edge, and wherein the at least one cutting edge hasa negative rake angle, a first clearance angle, and a wedge angle, avalue of the negative rake angle in a first region of the first cuttingedge end has a different value than in a second region of the secondcutting edge end, the first clearance angle in the first region of thefirst cutting edge end has a different value than in the second regionof the second cutting edge end, and the wedge angle along the cuttingedge profile is constant along an entire length from the first cuttingedge to the second cutting edge end.
 2. The milling head according toclaim 1, wherein along the cutting edge profile, there are no twodistinct points on the at least one cutting edge where the at least onecutting edge has identical values for at least one of the negative rakeangles and the first clearance angles.
 3. The milling head according toclaim 1, wherein a value of at least one of the negative rake angles andthe first clearance angles varies continuously along the cutting edgeprofile of the at least one cutting edge.
 4. The milling head accordingthe claim 1, wherein a value of at least one of the negative rake anglesand the first clearance angles varies linearly along the cutting edgeprofile of the at least one cutting edge.
 5. The milling head accordingto claim 1, wherein a value of the negative rake angle in the firstregion of the first cutting edge end is smaller than in the secondregion of the second cutting edge end, and/or the first clearance angleis smaller in the first region of the first cutting edge end than in thesecond region of the second cutting edge end.
 6. The milling headaccording to claim 1, wherein a value of the negative rake angleincreases along the cutting edge profile of the at least one cuttingedge to an extent to which the first clearance angle also increases. 7.The milling head according to claim 1, wherein a width of the rake facein the first region of the first cutting edge end is greater than in thesecond region of the second cutting edge end.
 8. The milling headaccording to claim 1, wherein a first width of the rake face in thefirst region of the first cutting edge end is at most 0.4 and/or asecond width of the rake face in the second region of the second cuttingedge end is at least 0.1 mm.
 9. The milling head according to claim 1,wherein the cutting edge profile of the at least one cutting edge isselected from a group consisting of straight, curved, spiral, andcombinations thereof, and wherein the cutting edge profile extendsparallel to the imaginary center axis.
 10. The milling head according toclaim 1, wherein: a) the value of the negative rake angle in the firstregion of the first cutting edge end is from at least 10° to at most19°and/or in the second region of the second cutting edge end from atleast 20° to at most 30° and/or b) the first clearance angle in thefirst region of the first cutting edge end is from at least 5° to atmost 10° and/or in the second region of the second cutting edge end isfrom at least 15° to at most
 20. 11. The milling head according to claim1, wherein a second flank face adjoins the first flank face on acircumference, to which a second clearance angle is assigned.
 12. Themilling head according to claim 11, wherein the second clearance anglealong the cutting edge profile is constant.
 13. The milling headaccording to claim 1, wherein the milling head comprises a main body,and wherein the at least one cutting edge is formed: a) on the mainbody, or b) on a cutting insert connected to the main body.
 14. Themilling head according to claim 1, in combination with a ball trackmilling cutter.
 15. The milling head according to claim 1, wherein thecutting edge profile of the at least one cutting edge is selected from agroup consisting of straight, curved, spiral, and combinations thereof,and wherein the cutting edge profile defines an angle relative to theimaginary center axis.
 16. The milling head according to claim 11,wherein the second clearance angle is greater than the first clearanceangle everywhere along the cutting edge profile.
 17. The milling headaccording to claim 12, wherein the second clearance angle is at least16° and at most 21°.
 18. The milling head according to claim 13, whereinthe at least one cutting edge is formed on the cutting insert connectedto the main body and soldered to the main body.